Field
The present disclosure relates to measuring non-contact impedance (complex resistivity) measurement adopting the transformer principle. In particular, the disclosure relates to impedance and complex resistivity measurements in concrete and other materials transformed to a solid phase from a liquid phase.
Background
A hardened hydraulic cement-based material, such as Portland cement, is produced by the hydration reaction which is a complex chemical, physical and mechanical process that starts as soon as water is mixed with cement particles and turns the water-cement mixes into a stone-like material. This complex process is referred as to the hydration of cementitious materials. The main characteristic of the hydration is the reduction of porosity accompanied by the formation of the hydration products. The continuously evolving network of pores determines the ultimate physical and mechanical properties of the cementitious materials, including strength, permeability and durability. Considerable attention has been focused on the pore structure characterization. Experimental methods to measure pore structure characteristics of such cements include water adsorption, mercury intrusion porosimetry (MIP), helium pycnometry, solvent replacement, nuclear magnetic resonance relaxation (NMR), scanning electronic microscope (SEM), transmission electronic microscope (TEM), X-ray diffraction (XRD), and small angle X-Ray scattering. Among the several techniques that allow investigating the evolution of the microstructure of cement-based materials, those based on monitoring the electrical properties during the cement hydration process have received attention.